Alcoholic beverage drinkers can easily determine when they have drunk too much to drive. They can consult a simple chart that estimates blood alcohol concentration (BAC) based on gender, weight, and how many standard drinks they’ve had. Unfortunately, such simple charts do not exist for marijuana. So how can medical cannabis users know when they are safe to drive in Illinois and not get charged with driving under the influence?

Under current Illinois law, a THC level over 5 nanograms per milliliter of whole blood is per se (sufficient by itself) proof of marijuana DUI for most drivers. Illinois medical cannabis cardholders are exempt from the THC limit, but they can still be charged with DUI based on other evidence of impairment, primarily failure on the standardized field sobriety tests (walk-and-turn, one-leg stand, and follow-the-object eye test).

This article provides a basic explanation of how the body processes THC, the psychoactive compound in marijuana associated with driver impairment, to help users understand how marijuana may affect their ability to drive.

The effect of alcohol consumption on the ability to drive safely has been studied intensely for over 60 years. Scientists have developed tests of blood alcohol concentration (BAC), including breathalyzers and blood tests, that are accurate enough to be fully accepted by American courts. Scientific studies have proven that alcohol impairment begins with the first drink; that the higher a person’s BAC level is, the more impaired their driving is; and that .08 is a level at which driving is so impaired as to pose a significant danger to public safety.

But when it comes to marijuana, such conclusive research does not yet exist. Yes, the level of THC, marijuana’s main psychoactive component, in the blood can be measured. But, different from alcohol, THC can be present in the blood long after its psychoactive effect has worn off. There is currently no test that can differentiate “active” THC that would impair driving from “inactive” THC that would not. Nor is there clear and convincing research showing what level of THC results in impaired driving, or widespread agreement on what the legal limit should be.

So how can Illinois arrest, much less convict, people of driving under the influence of marijuana?

Just recently, there has been a novel way for law enforcement to determine whether or not a person has been driving after using drugs. To test for alcohol in the system, the standardized breath test is often administered. Then, if the driver who was pulled over had been drinking before going behind the wheel, he or she may be charged with a DUI, which could cause undesired consequences, such as lost driving privileges, loss of the vehicle, or even lost employment opportunities.

What Is This New Test?

Drunk driving is often very obvious to detect, with the slurred speech and the smell of alcohol on the driver. However, if the driver has been using marijuana, prescription drugs, and heroin, there are other ways that these drugs must be detected.

Driving under the influence of alcohol and driving under the influence of marijuana can cause serious injuries and even death if an accident was ever to occur. However, how each substance is measured is different. Individuals may use marijuana for medicinal purposes, but they still need to be aware of the potential dangers of driving after using the substance. Individuals are alarmed at what they find out about the dangers of driving after using marijuana.

What to Know About Marijuana Use and Driving

Three years ago, in 2014, there were about 7,000 individuals who started using marijuana or similar substances every day. During the weekend nights, as many as 13 percent of all drivers have some amount of marijuana in their system, compared to only nine percent of weekend nighttime drivers in 2007. Alcohol and marijuana are the two biggest contributors to drugged driving.

Much of what we do while on the road can be categorized as distracting—talking, texting, eating. These are just a few examples of everyday occurrences that keep us from driving at our best. Media outlets and printed articles distribute the impact of these distractions to a broad audience. However, one less discussed modifier is marijuana, perhaps because it is a controlled substance.

Although marijuana is not legal recreationally at this point in Illinois, there are bills in motion aiming to legalize the substance for consenting adults. Many have concerns over how this will affect DUI Marijuana charges. Yet how do drugs affect our driving performance?

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